The invention relates to initiation of explosive devices for use in various applications, including wellbore applications.
In completing a well, different types of equipment and devices are run into the well. For example, a perforating gun string can be lowered into a wellbore proximal a formation that contains producible fluids. The perforating string is fired to create openings in surrounding casing as well as to extend perforations into the formation to establish production of fluids. Other completion devices that may be run into a wellbore include packers, valves, and other devices.
A detonating cord is one type of initiator that has been used to detonate explosives in perforating guns as well as other devices. In a perforating gun, shaped charges are coupled to a detonating cord, which when initiated causes the shaped charges to fire. A detonating cord detonates at a certain speed (e.g., about 7 to 8.5 kilometers per second). As a result, consecutive shaped charges may fire with a typical delay of about 5 to 10 microseconds of one another, depending on the distance between successive charges. Although the detonation wave traveling down the cord is relatively fast, some separation between charges is needed to reduce the likelihood that the detonation of one charge interferes with the subsequent detonation of an adjacent charge. The separation distance required for proper firing of charges is usually about one charge diameter, although distance may vary depending on the application.
In some arrangements of perforating guns, multiple charges may be arranged in a plane so that simultaneous firing of charges in one plane is possible. However, some separation is still needed between charge planes to prevent charges in one plane from interfering with the firing of charges in another plane. The shot separation requirement reduces the shot density of a perforating gun. Increasing the shot density of a perforating gun typically increases the productivity of a well. Most modem perforating guns are designed to give the maximum shot density possible within the limitations of the detonating cord. The detonating cord may be initiated by a percussion detonator or by an electrical detonator.
Another type of initiator for activating explosive devices such as shaped charges include exploding foil initiators (EFIs), which is electrically activated. An EFI typically includes a metallic foil connected to a source of electric current. A reduced neck section having a very small width is formed in the foil, with an insulator layer placed over a portion of the foil including the neck section. When a high current is applied through the neck section of the foil, the neck section explodes or vaporizes. This causes a small flyer to shear from the insulator layer, which travels through a barrel to impact an explosive to initiate a detonation. Other electrically activated initiators include exploding bridgewire (EBW) initiators, exploding foil xe2x80x9cbubble activatedxe2x80x9d initiators, and others.
Multiple EFIs may be coupled to an electrical line and placed in close proximity with shaped charges. An activation current may be generated in the electrical line to activate the multiple EFIs. Such an arrangement allows multiple explosives to be initiated with nanosecond simultaneity. However, in one prior EFI system, the electric power is provided by a power source that includes a CMF (compressed magnetic field) power source capable of providing high current. A flat flexible cable is used to distribute the relatively high power to the EFIs. However, providing such relatively high power in a downhole environment may be difficult to accomplish.
In another distributed architecture in which lower power is employed to activate initiators, semiconductor bridge (SCB) initiators are employed. The SCB initiators are included in corresponding shaped charges, with an electrical wire routed to each SCB initiator. Although SCB initiators are useful for some purposes, EFI or EBW initiators are more desirable for some applications. For example, although SCB initiators require less power, they are generally slower than typical EFI and EBW initiators. As a result, desired simultaneously of detonation of explosives may not be achievable with SCB initiators.
A need thus exists for an initiation device including EFI, EBW, or other like initiators that can be activated with reduced electrical power to detonate explosive devices.
In general, according to one embodiment, a tool includes a plurality of explosive devices and a plurality of initiator devices each including a bridge-type initiator and adapted to detonate a corresponding explosive device. Each initiator device includes an energy source, and an electrical cable is adapted to energize the energy source in each initiator device. Each energy source provides activation power to a corresponding bridge-type initiator.
Other features and embodiments will become apparent from the following description and from the claims.